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Disc Pain and Sciatica

People with back problems often talk about having a 'slipped disc'. However, the majority of pain in the back which gets labelled as this is not from the disc.  Relatively speaking, younger people from 30-60 are more likely to experience back pain from the disc space itself (e.g. lumbar disc herniation or degenerative disc disease). Older adults (over 60) are more likely to suffer from pain related to joint degeneration (e.g. osteoarthritis, spinal stenosis).

Disc structure

As discussed in the "Structure of the Spine" page, each pair of vertebrae are separated by an intervertebral disc.  This provides cushioning and flexibility between the vertebral bodies.  The disc has two main components and can best be thought of as a structure similar to a cross-ply tyre  providing the strong resilient outer part of the disc.  This is called the annulus fibrosus.  Inside this, inside the disc, there is a jelly-like substance called the nucleus pulposus, which has a consistency like a half-sucked fruit pastille.

Disc degeneration

One of the changes that happens with wear and tear (degeneration) of the disc is that the water content of the nucleus reduces.  This does not imply that the disc is leaking, but is a sign of degeneration.  This is evident on MRI scans where the disc appears less light-coloured than normal.  

Sometimes, due to cumulative wear and tear, the annulus can become weakened and, rather like a worn tyre bulging, it can develop a bulge.  Because of the way the back moves this is more commonly at the back of the disk, either in the midline or to one side.  Sometimes, a split in the annulus can develop.  These processes can cause pain, and the bulge of the disc can contribute to tightness of the spaces (foramina) through which the nerve roots emerge between the backs of the vertebrae or of the spinal canal. The former can cause nerve pain referring down the leg (sciatica) or arm, and the latter can contribute to spinal stenosis.  

Sometimes, through a split in the annulus, some of the nucleus pulposus can squeeze out (like toothpaste from a hole in the tube).  This is called a disc prolapse or prolapsed intervertebral disc (PID - be aware that these initials are also sometimes used medically in another context for pelvic inflammatory disease).  This disc prolapse can press on or irritate the nerve roots giving rise to nerve pain.  This, in the distribution of the sciatic nerve, is called Sciatica

Sciatica

Sciatica is the name given to pains referred down the leg because the sciatic nerve from the spinal cord has been pinched or irritated by damage to the back - sometimes by a prolapsed disc pressing on it.  The sciatic nerve is the main nerve in the leg and the largest in the body. It runs from the base of the spine, along the back of the thigh to the knee, where it divides into branches that supply the lower leg and foot..  Sciatic pain is usually caused by compression of this nerve root at the point where it leaves the spine.   In young and early middle-aged adults, the most common cause of sciatica is a prolapsed intervertebral disc in the lumbosacral area of the lower back.  In older people, changes in the spine due to wear and tear (osteoarthritis) may be responsible either by causing localised pressure on the nerve in the foramina or by spinal stenosis.

Sciatica normally only affects one leg. The pain may be felt in the buttock, down the back of the leg, below the knee and in the foot. If there is back pain, it is usually less severe than the pain down the leg. Such pain can be mild or severe; it may be persistent or come in spasms.  People with sciatica may also experience numbness, tingling and muscle weakness in the affected leg. It can be worse when you cough or move, and is sometimes accompanied by low back pain.

The majority of disc prolapses get better on their own due to the body's immune defenses breaking down the disc material.  It is extremely unlikely that manipulation of the back will remove or reduce the disc material.

Other pains can refer down the leg in the sciatic nerve distribution that are not caused by disc prolapse or stenosis.  Sometimes, unfortunately, pain can persist after a prolapse or other cause, even after surgery, due either to scarring around the nerve or else the central nervous system connections of the nerve can "remember" the problem and continue to behave abnormally, giving rise to pain.  In addition, some other pain sources such as the joints in the spine, being supplied by branches of the nerve roots of the sciatic nerve, can give pain referring in a similar distribution, and myofascial trigger points in some of the muscles around the buttock and thigh (notably in the piriformis muscle as "piriformis syndrome") can give pain that imitates sciatica.

 

Sciatica treatments

Sciatica frequently resolves without treatment. The following actions and treatments are sometimes used:

Exercise and as much normal function as possible -  the evidence is that it is beneficial to continue with normal activities as far as possible.  Initially, this may be difficult if the pain is bad, but it is important to resume gentle activity as soon as possible.  It is important to be aware that discomfort does not mean you are injuring yourself - "Hurt does not equal harm".

However, move around as soon as possible, and get back into normal activities as soon as you are able. As a rule, don't do anything that causes a lot of pain. However, you will have to accept some discomfort when you are trying to keep active. 

As the page linked below comments: Setting a new goal each day may be a good idea - for example, walking around the house on one day, a walk to the shops the next, etc.  In the past, advice used to be to rest until the pain eases. It is now known that this was wrong. You are likely to recover more quickly and are less likely to develop chronic (persistent) back pain if you keep active when you have back pain rather than rest a lot. Also, sleep in the most naturally comfortable position on whatever is the most comfortable surface. (Advice given in the past used to be to sleep on a firm mattress. However, there is no evidence to say that a firm mattress is better than any other type of mattress for people with back pain.)

Painkilling Medication - these should be used regularly to facilitate movement.  Sometimes other approaches like a TENS machine can be helpful.

Physical treatments - as the page linked below comments: "Some people visit a physiotherapist, chiropractor, or osteopath for manipulation and/or other physical treatments. It is debatable whether physical treatments would help all people with a prolapsed disc. However, physical treatments provide some short-term comfort and hasten recovery in some cases".

Epidural Injections - these have often been used in the early stages of sciatica.  The aim is to apply a locally acting steroid plus local anaesthetic to the affected nerves to try to reduce the swelling, inflammation and the irritability of the nerve.  The evidence for long-term relief from epidurals is not very strong, but they are still sometimes used.

Surgery -  may be an option in some cases.  Surgery may be considered if the symptoms have not settled after about six weeks or so. This is the minority of cases as, in about 93% of cases, the symptoms will improve spontaneously.  Some studies have suggested that early surgery may be more beneficial than delaying, but against this has to be set the risks of surgery and the need for recovery postoperatively, and the fact that surgery does not always help.

 

 

Links

Patient.co.uk page on sciatica and disc pain including red flags, and on prolapsed intervertebral disc.

Information sheet on Lumbar Discectomy and Decompression from the British Association of Spinal Surgeons

 

 

 

 

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Pain Service Website, Gloucestershire Hospitals NHS Foundation Trust
Webmaster Dr J G de Courcy, Consultant in Pain Medicine and Anaesthesia
email: pain.webmaster[at]glos.nhs.uk

Page updated 15/02/2016